1. Field of the Invention
This invention relates to compounds, to processes of their preparation, to pharmaceutical compositions containing them and to their medical use as agonists at kappa opioid receptors.
The present invention also relates to compositions and method for the treatment and/or prevention of itch, also known as pruritus, which has many causes. The compositions, which are formulated for topical and systemic administration, contain kappa opiate receptor agonists that are substantially devoid of central nervous system effects, and, thus, have very little, if any potential for producing side effects associated with centrally acting kappa opiate receptor agonists.
2. Reported Developments
A) Kappa (xcexa)-receptor Agonists as Analgesics
Opium and its derivatives are potent analgesics that also have other pharmacological effects, and exert their effects by interacting with high-affinity receptors.
It has been shown by investigators that there are at least three major opioid receptor types in the central nervous system (hereinafter CNS) and in the periphery. These receptors, known as mu (xcexc), delta (xcex4) and kappa (xcexa), have distinct pharmacological profiles, anatomical distributions and functions. [See, for example: Wood, P. L., Neuropharmacology, 21, 487-497, 1982; Simon, E., J Med. Res. Rev., 11, 357-374, 1991; Lutz et al., J. Recept. Res. 12, 267-286; and Mansour et al., Opioid I, ed. Herz,. A. (Springer, Berlin) pp. 79-106, 1993.] The xcex4 receptors are abundant in CNS and mediate analgesia, gastrointestinal motility and various hormonal functions. The xcexc receptors bind morphine-like drugs and mediate the opiate phenomena associated with morphine, including analgesia, opiate dependence, cardiovascular and respiratory functions, and several neuroendocrine effects.
The xcexa receptors have a wide distribution in CNS and mediate a spectrum of functions including the modulation of drinking, water balance, food intake, gut motility, temperature control and various endocrine functions. They also produce analgesia. [See, for example: Leander et al., J. Pharmacol. Exp. Ther. 234, 463-469, 1985; Morley et al., Peptides 4, 797-800, 1983; Manzanares et al., Neuroendocrinology 52, 200-205, 1990; and Iyengar et al., J. Pharmacol. Exp. Ther., 238, 429-436, 1986.]
Most clinically used opioid analgesics such as morphine and codeine act as xcexc receptor agonists. These opioids have well-known, undesirable and potentially dangerous dependence forming side effects. Compounds which are xcexa-receptor agonists act as analgesics through interaction with xcexa opioid receptors. The advantage of these agonists over the classical xcexc receptor agonists, such as morphine, lies in their ability to cause analgesia while being devoid of morphine-like behavioral effects and addiction liability.
A large number of classes of compounds which act as agonists at xcexa opioid receptors have been described in the art including the following illustrative classes of compounds.
U.S. Pat. No. 4,065,573 discloses 4-amino-4-phenylcyclohexane ketal compounds having analgesic activity.
U.S. Pat. No. 4,212,878 discloses phenylacetamide derivatives having analgesic properties and reduced physical dependence liability properties, relative to morphine and methadone.
U.S. Pat. No. 4,145,435 discloses N-(2-amino-cycloaliphatic)-phenylacetamide compounds having analgesic activity and narcotic antagonist activity.
U.S. Pat. No. 4,098,904 discloses N-(2-amino-cycloaliphatic)-benzoamides and naphthamides useful for relieving pain.
U.S. Pat. No. 4,359,476 discloses substituted cycloalkane-amides useful as analgesics and having low abuse liability.
U.S. Pat. No. 4,438,130 discloses 1-oxa-, aza- and thia-spirocyclic compounds having analgesic activity, low physical dependence and abuse liability properties and little dysphoric inducing properties.
U.S. Pat. No. 4,663,343 discloses substituted naphthalenyloxy-1,2-diaminocyclohexyl amides as analgesics.
U.S. Pat. No. 4,906,655 discloses 1,2-cyclohexylaminoaryl amides having high kappa-opioid affinity, selectivity and potency and useful as analgesics, diuretics, anti-inflammatory and psychotherapeutic agents.
B) Kappa (xcexa)-receptor Agonists as Anti-Pruritic Agents
The prior art has investigated the physiology and treatment of pruritus as illustrated hereunder.
Itch is a well known sensory state associated with the desire to scratch As with pain, itch can be produced by a variety of chemical mechanical, thermal or electrical stimuli. In addition to the difference in the sensory quality of itch and pain, they also differ in that (1) itch, unlike pain, can only be evoked from the superficial layers of skin, mucosa, and conjunctiva, and (2) itch and pain usually do not occur simultaneously from the same skin region; in fact, mildly painful stimuli, such as scratching, are effective in eliminating itch. In addition, the application of histamine to skin produces itch but not pain. Itch and pain are further dissociated pharmacologically: itch appears to be insensitive to opiate and non-steroidal anti-inflammatory drug (NSAID) treatment, both of which are effective in treating pain.
Although itch and pain are of a class in that both are modalities of nociception transmitted by small unmyelinated C fibers, evidence that itch is not just a variety of low-threshold pain is overwhelming. Itch leads to the reflex or urge to scratch; pain leads to withdrawal. Itch occurs only in the skin; pain arises from deeper structures as well. Heat may stop pain but usually increases pain. Removal of the epidermis eliminates itch but causes pain. Analgesics, particularly opioids, relieve pain but often cause itch (see, for example J. Am. Acad. Derm. 24: 309-310, 1991). There can be no doubt that itching is of eminent clinical importance; many systemic and skin diseases are accompanied by persistent or recurrent itch attacks. Current knowledge suggests that itch has several features in common with pain but exhibits intriguing differences as well (see, for example, W. Magerl, IASP Newsletter, pp. 4-7, Sept/Oct 1996).
McMahon et al. (TINS, Vol. 15, No. 12, pp. 497-501, 1992) provides a description of stimuli (Table a) and a comparison of the established features of itch and pain (Table b):
Experimental focal itch stimuli are surrounded by a halo of seemingly unaffected tissue where light tactile stimuli are capable of eliciting itch-like sensations. The term itchy skin or alloknesis has been coined for these secondary sensations that are reminiscent of the features of secondary hyperalgesia evolving around a painful focus. A crucial observation is that itch and pain usually do not coexist in the same skin region and a mild noxious stimulus such as scratching is in fact the singly most effective way to abolish itch. This abolition of itch can be prolonged producing an xe2x80x98antipruritic statexe2x80x99. Although mild scratch is often not painful, microneurographic recordings from humans have directly determined that such stimuli are among the most effective ways to excite cutaneous unmyelinated nociceptive afferents. (See, for example:
Shelly, W. B. and Arthur, R. P. (1957) Arch. Dermatol. 76, 296-323;
Simone, D. A. et al. (1987) Somatosens. Res. 5, 81-92;
Graham, D. T. , Goodell, H. and Wolff, H. G. (1951) J. Clin. Invest. 30, 37-49;
Simone, D. A., Alreja, M. and LaMotte, R. H. (1991) Somatosens Mot. Res. 8, 271-279;
Torebjxc3x6rk, E (1985) Philos. Trans. R. Soc. London Ser. B 308, 227-234; and
Vallbo, A. B., Hagbarth, K. E., Torebjxc3x6rk, H. E. and Wallin, B. G. (1979) Physiol. Rev. 59, 919-957).
Physiologically, there is evidence that substance P released from nociceptor terminals can cause the release of histamine from mast cells. Activation of mast cells, with release of the pruritogen histamine, occurs in immediate type hypersensitivity diseases, such as anaphylactic reactions and urticaria. Urticarial eruptions are distinctly pruritic and can involve any portion of the body, and have a variety of causes beyond hypersensitivity, including physical stimuli such as cold, solar radiation, exercise and mechanical irritation. Other causes of pruritus include: chiggers, the larval form of which secretes substance that creates a red papule that itches intensely; secondary hyperparathyroidism associated with chronic renal failure; cutaneous larva migrans, caused by burrowing larvae of animal hookworms; dermal myiasis, caused by maggots of the horse botfly, which can afflict horseback riders; onchocerciasis (xe2x80x9criver blindnessxe2x80x9d) caused by filarial nematodes; pediculosis, caused by lice infestations; enterobiasis (pinworm) infestations, which afflict about 40 million Americans, particularly school children; schistosome dermatitis (swimmer""s itch); and asteatotic eczema (xe2x80x9cwinter itchxe2x80x9d). The role of histamine or other endogenous pruritogens in mediating itch associated with these and other pruritic conditions, such as atopic dermatitis, it is not yet well established. For atopic dermatitis, in particular, it appears that itch is not inhibited by antihistamines, but by cyclosporin A, a drug which inhibits the production of cytokines which have been proposed as potential pruritogens.
Current therapies for the treatment of itch include a variety of topical and systemic agents, such as steroids, antihistamines, and some psychotherapeutic tricyclic compounds, such as doxepin hydrochloride. Many such agents are listed in PDR Generics (see Second Edition, 1996, p. cv for a listing of said agents). The limitations of these agents are well known to medical practitioners, and are summarized in the xe2x80x9cWarningsxe2x80x9d and xe2x80x9cPrecautionsxe2x80x9d sections for the individual agents listed in PDR Generics. In particular, the lack of complete efficacy of antihistamines is well known, but antihistaines are frequently used in dermatology to treat pruritus due to urticaria, atopic dermatitis, contact dernatitis, psoriasis, and a variety of other conditions. Although sedation has been a frequent side effect of conventional systemically administered antihistamines, a new generation of antihistamines have been developed that are nonsedating, apparently due to their inability to cross the blood-brain barrier.
Intravenous administration of opiate analgesics, such as morphine and hydromorphone has been associated with pruritus, urticaria, other skin rashes, wheal and flare over the vein being injected. These itch and itch-related reactions are believed to be due to a histamine-releasing property of these opiates, via mast cell degranulation. These opiates are thought to act upon the mu subtype of opiate receptor, but the possibility of interactions at the other principal opiate receptor subtypes (delta and kappa) cannot be excluded since these and other pruritogenic analgesics are not pure mu agonists. The cellular loci of the receptor type(s) mediating the itching effect is not known, although the mast cell is a possible candidate since opiates cause histamine release from these cells. However, some investigators have suggested that the frequent inability of antihistamines to block morphine-induced itching suggests a non-histaminergic mediation of opiate-induced itchingxe2x80x94a mechanism which could involve central opiate receptors. Although i.v. morphine only occasionally results in generalized itching (in about 1% of patients), pruritus is more prevalent in opiate analgesia with epidural (8.5%) or intraspinal (45.8%) administration. (See, for example: Bernstein et al., xe2x80x9cAntipruritic Effect of an Opiate Antagonist, Naloxone Hydrochloridexe2x80x9d, The Journal of Investigative Dermatology, 78:82-83, 1982; and Ballantyne et al., xe2x80x9cItching after epidural and spinal opiatesxe2x80x9d, Pain, 33: 149-160, 1988.)
To date, treatment with opiates has not only proven useless in the treatment of itch, but appears to exacerbate itch in man. The consistent findings form human studies indicate that whether by central or peripheral mechanisms, opiates appear to promote rather than prevent itching, and that opiate antagonists have anti-pruritic activity.
Human clinical studies have generally shown that opiates cause itching and there is evidence that these effects can be reproduced in animal models, where itching sensations per se cannot be reported, but scratching behavior can be observed. (See, for example: Thomas et al., xe2x80x9cMicroinjection of morphine into the rat medullary dorsal horn produces a dose-dependent increase in facial-scratchingxe2x80x9d, Brain Research, 195: 267-270, 1996; Thomas et al., xe2x80x9cEffects of central administration of opioids on facial scratching in monkeysxe2x80x9d, Brain Res., 585: 315-317, 1992; and Thomas et al., xe2x80x9cThe medullary dorsal horn: A site of action of opioids in producing facial scratching in monkeysxe2x80x9d, Anesthesiology, 79: 548-554, 1993).
We have now surprisingly discovered that kappa agonist compounds, which are substantially devoid of central nervous system effects, in pharmaceutically acceptable vehicles for systemic and topical formulations possess anti-pruritic activity in addition to anti-hyperalgesic activity.
8-12. EPO 147,085
EPO 207,773
U.S. Pat. No. 4,855,316
U.S. Pat. No. 4,906,655 and
EPO 372,466
disclose indene, indole, benzofuran and benzothiophene analogs comprising: 
wherein Z can be CH2, NH, S or O, but there is no xe2x80x94NH2 substituent; 
wherein Z is CH2, NH, S, R, RC and R3 is simple alkyl substituents; 
13. WO 92/20657 discloses compounds of the formula comprising: 
wherein
or Z is 
xe2x80x83wherein
p=0-20;
R3=xe2x80x94H or xe2x80x94Ac;
X2=xe2x80x94CO2H; xe2x80x94NHSO2CH3; NHP(O)(OBn)2; NHP(O)(OH)2; xe2x80x94OP(O)(OBn)2; or OP(O)(OH)2;
X and Y are independently
xe2x80x94CH2NHSO2CH3, xe2x80x94CH2NHP(O)(OBn)2, xe2x80x94CH2NHP(O)(OH)2, xe2x80x94CH2OP(O)(OBn)2, xe2x80x94CH2OP(O)(OH)2, xe2x80x94(CH2)qO(CH2)qCO2H xe2x80x94(CH2)qO(CH2)qSO3H, xe2x80x94(CH2)qO(CH2)qCHNHOH. xe2x80x94CH2NHC(S)NHCH(CO2H)(CH2)qCO2H or 
xe2x80x83wherein
r=1-20
R4=xe2x80x94H or xe2x80x94Ac
X3=xe2x80x94CO2H; xe2x80x94NHSO2CH3; xe2x80x94NHP(O)(OBn)2; xe2x80x94NHP(O)(OH)2; xe2x80x94OP(OXOBn)2; or xe2x80x94OP(O)(OH)2,
The compounds of formula II have the following structure: 
wherein
n=1-3, where n=1 is preferred
R1 and R2 are independently=CH3; xe2x80x94(CH2)m, where m=4-8, m=4 is most preferred; xe2x80x94CH2CH(OH)(CH2)2xe2x80x94; CH2CH(F)(CH2)2xe2x80x94; xe2x80x94(CH2)2O(CH2)2xe2x80x94; or xe2x80x94(CH2)2CHxe2x95x90CHCH2xe2x80x94;
Ar=unsubstituted or mono- or di-substituted phenyl wherein said substituents are selected from the group consisting of halogen, OCH3, SO2CH3, CF3, amino, alkyl, and 3,4-dichloro; benzothiophenyl; benzofuranyl; naphthyl; diphenyl methyl; or 9-fluorene;
X4 and X5 are independently
xe2x80x94OP(O)(OBn)2; xe2x80x94OP(O)(OH),; xe2x80x94CO2H; xe2x80x94SO3H; xe2x80x94SO3H; xe2x80x94O(CH2)nCO2H; xe2x80x94NHSO2CH3; xe2x80x94CONH(CH2),CO2H; or xe2x80x94SO2NH(CH2),CO2H; wherein
s=1-5
or X4 and X5 are independently 
xe2x80x83wherein
t=1-20
R5=xe2x80x94H or xe2x80x94Ac
X6=xe2x80x94CO2H; xe2x80x94NHSO2CH; xe2x80x94NHP(O)(OBn)2; xe2x80x94NHP(O)(OH )2; OP(O)(OBn)2; or xe2x80x94OP(O)(OH)2.
The compounds of formula IIA have the following structure: 
wherein
n=1-3, where n=1 is preferred R1 and R2 are independently=CH3; xe2x80x94(CH2)m, where m=4-8, m=4 is most preferred; xe2x80x94CH2CH(OR)(CH2)2xe2x80x94 wherein R is H, alkyl, acyl or aroyl; CH2CH(F)(CH2)2xe2x80x94; xe2x80x94(CH2)2O(CH2)2xe2x80x94; or xe2x80x94(CH2)2CHxe2x95x90CHCH2xe2x80x94; Ar=mono- or di-substituted phenyl; wherein said substituents are selected from the group consisting of halogen, OCH3, OH, SO2CH3, CF3, NH2, alkyl, CN, unsubstituted and substituted sulfamoyl groups;
Ar may also be substituted with xe2x80x94NH(CH2)uCO2Rxe2x80x2; xe2x80x94NH(CH2)u(CHxe2x95x90CH)u(CH2)CO2Rxe2x80x2; xe2x80x94NHCO(CH2)u(CHxe2x95x90CH)u(CH2)uCO2Rxe2x80x2; xe2x80x94NHP(O)(OBn)2; xe2x80x94NHP(O)(ORxe2x80x2)2; xe2x80x94(CH2)uNHSO2CH3; xe2x80x94(CH2)uNHC(S)NHCH(CO2Rxe2x80x2)(CH2)uCO2Rxe2x80x2; xe2x80x94CONHOH; or CH2)uCONHOH;
xe2x80x83wherein
u=0-5;
Rxe2x80x2=H or lower alkyl;
or Ar is 
X4 and X5 are independently H; halogen; OH; OCH3; CF3; NO2; NH2; amino substituted with acyl, carbamate, alkyl or aryl sulfonates; CORxe2x80x2 where Rxe2x80x2 is OH, amide, alkoxy, aryloxy or heteroaryloxy.
Compounds of formula (IIA) have at least one chiral center and may exist in more than one diastereoisomeric form The invention includes within its scope all enantiomers, and diastereosomers and the mixtures thereof.
The compounds of formula III have the following structure: 
wherein
n=1-3, where n=1 is preferred R1 and R2 are independently CH3; xe2x80x94(CH2)m, where m=4-8, mr=4 is most preferred; xe2x80x94CH2CH(OH)(CH2)2xe2x80x94; CH2CH(F)(CH2)2xe2x80x94; xe2x80x94(CH2)2O(CH2)2xe2x80x94; or xe2x80x94(CH2)2CHxe2x95x90CHCH2xe2x80x94;
Ar=unsubstituted or mono- or di-substituted phenyl wherein said substituents are selected from the group consisting of halogen, OCH3, SO2CH3, CF3, amino, alkyl, and 3,4-dichloro; benzothiophenyl; benzofuiranyl; naphthyl; diphenyl methyl; or 9-fluorene;
X7 is
xe2x80x94NHSO2CH3; xe2x80x94NHP(O)(OBn)2; xe2x80x94NHP(O)(OH2; xe2x80x94(CH2)uNSO2CH3; xe2x80x94(CH)uNHC(S)NHCH(CO2H)(CH2)uCO2H; xe2x80x94CONHOH; or xe2x80x94(CH2)uCONHOH;
xe2x80x83wherein
u=1-5
or X7 is 
The compounds of formula IIIA have the following strucutre: 
wherein
n=1-3, where n=1 is preferred; R1 and R2 are independently=CH3; xe2x80x94(CH2)m, where m=4-8, m=4 is most preferred; xe2x80x94CH2CH(OR)(CH2)2xe2x80x94, wherein R=H, alkyl, acyl or aroyl; CH2CHO(CH2)2xe2x80x94; xe2x80x94(CH2)2O(CH2)2xe2x80x94; or xe2x80x94(CH2)2CHxe2x95x90CHCH2;
Ar=mono- or di-substituted phenyl; wherein said substituents are selected from the group consisting of halogen, OCH3, OH, SO2CH3, CF3, NH2, alkyl, CN, unsubstituted and substituted sulfamnoyl groups;
Ar may also be substituted with xe2x80x94NH(CH2)uCO2Rxe2x80x2; xe2x80x94NH(CH2)u(CHxe2x95x90CH)u(CH2)CO2Rxe2x80x2; xe2x80x94NHCO(CH2)u(CHxe2x95x90CH)u(CH2)uCO2Rxe2x80x2; xe2x80x94NHP(O)(OBn)2; xe2x80x94NHP(O)(OR)2; xe2x80x94(CH2)uNHSO2CH3; xe2x80x94(CH2)uNHC(S)NHCH(CO2Rxe2x80x2)(CH2)uCO2Rxe2x80x2; xe2x80x94CONHOH; or CH2)uCONHOH;
xe2x80x83wherein
u=0-5;
R=H or lower alkyl;
or Ar is 
X7 is H; halogen; OH; OCH3; CF3; NO2; NH2; amino substituted with acyl, carbamate, alkyl or aryl sulfonates; CORxe2x80x2 where Rxe2x80x2 is OH, amide, alkoxy, aryloxy or heteroaryloxy.
Compounds of formula (IIIA) have at least one chiral center and may exist in more than one diastereoisomeric fornl The invention includes within its scope all enantiomers, and diastereosomers and the mixtures thereof.
The compounds of formula IV have the following structure: 
wherein
n=1-3, where n=1 is preferred R1 and R2 are independently=CH3; xe2x80x94(CH2)m, where m=4-8, m=4 is most preferred; xe2x80x94CH2CH(OH)(CH2)2xe2x80x94; CH2CH(F)(CH2)2xe2x80x94; xe2x80x94(CH2)2O(CH2)2xe2x80x94; or xe2x80x94(CH2)2CHxe2x95x90CHCH2xe2x80x94;
R3 and R4 are independently H; OCH3; alkyl; or Cxe2x80x94O(CH2)2;
X9=1-4 substituents selected from the groups consisting of -halogen; xe2x80x94CF3; xe2x80x94OCH3; SO2NH(CH2)qCO2H; xe2x80x94CONH(CH2)qCO2H; xe2x80x94NH2; xe2x80x94NHSO2CH3; xe2x80x94NHP(O)(OBn)2; xe2x80x94NHP(O)(OH)2; xe2x80x94SO2CH3; xe2x80x94OP(O)(OBn)2; xe2x80x94OP(O)(OH)2; xe2x80x94CO2H; xe2x80x94O(CH2)qCO2H; xe2x80x94O(CH2)qSO3H, xe2x80x94O(CH2)qOPO3H2; wherein
q=1-20.
or X9 is 
xe2x80x83wherein
t=1-20
R5=xe2x80x94H or xe2x80x94Ac
X6=xe2x80x94CO2H; xe2x80x94NHSO2CH3; xe2x80x94NHP(O)(OBn)2; xe2x80x94NHP(O)(OH)2; xe2x80x94OP(O)(OBn)2; or xe2x80x94OP(O)(OH)2xe2x80x94.
The compunds of formula IVA have the following structure: 
wherein
n=1-3, where n=1 is preferred R1 and R2 are independently=CH3; xe2x80x94(CH2)m, where m=4-8, m=4 is most preferred; xe2x80x94CH2CH(OR)(CH2)2xe2x80x94; wherein R=H, alkyl, acyl, or aroyl; CH2CH(F)(CH2)2xe2x80x94; xe2x80x94(CH2)2O(CH2)2xe2x80x94; or xe2x80x94(CH2)2CHxe2x95x90CHCH2xe2x80x94;
R3 and R4 are independently H; OCH3; alkyl; or xe2x80x94O(CH2)2;
X9=1-4 substituents selected from the groups consisting of -halogen; xe2x80x94CF3; OH, xe2x80x94OCH3; xe2x80x94SO2NH(CH2)qCH3; xe2x80x94NH(CH2)qCORxe2x80x2; xe2x80x94NH(CH2)q(CHxe2x95x90CH)q(CH2)qCO2Rxe2x80x2; NH(CH)q(CHxe2x89xa1CH)q(CH)qCO2R; xe2x80x94NHCO(CH2)q(CHxe2x95x90CH)q(CH2)qCO2R; and xe2x80x94NHCO(CH)q(CHxe2x95x90CH)q(CH)qCO2Rxe2x80x2
xe2x80x83wherein
q=0-20
Rxe2x80x2=OH, lower alkyl, aryl ester or aryl amide.
Compounds of formula (IVA) have at least one chiral center and may exist in more than one diastereoisomeric form. The invention includes within its scope all enantiomers, and diastereosomers and the mixtures thereof
The meaning of the terms used in the specification and the claims, unless otherwise denoted, are as follows.
The terrn xe2x80x9calkylxe2x80x9d as used herein alone or as part of another group, denotes optionally substituted, straight and branched chain saturated hydrocarbon groups, preferably having 1 to 12 carbons in the normal chain, most preferably lower alkyl groups. Exemnplary unsubstituted groups include methyl, ethyl, propyl isopropyl n-butyl t-butyl, isobutyl, pentyl, hexyl, isohexyl, 4,4-dimethylpentyl, octyl, 2,2,4-trimethylpentyl, nonyl, decyl, undecyl, dodecyl and the like. Exemplary substituents include one or more of the following groups: halo, alkoxy, arylalkyloxy (e.g., benzyloxy), alkylthio, alkenyl alkynyl, aryl, cycloalkyl, cycloalkenyl, hydroxy, carboxyl (xe2x80x94COOH), amino, alkylamino, dialkylamnino, formyl, alkylcarbonyloxy, alkylcarbonyl heterocyclo, aryloxy or thiol (xe2x80x94SH). Preferred alkyl groups are unsubstituted alkyl, haloalkyl, arylalkyl, aminoalkyl. alkylarninoalkyl, dialkylaminoalkyl alkoxyalkyl aryloxyalkyl, hydroxyalkyl and alkoxyalkyl groups.
The term xe2x80x9clower alkylxe2x80x9d as used herein denotes such optionally substituted groups as described above for alkyl having 1 to 4 carbon atoms in the normal chain.
The terms xe2x80x9carxe2x80x9d or xe2x80x9carylxe2x80x9d as used herein or as part of another group, denote optionally substituted, homocyclic aromatic groups, preferably containing 1 or 2 rings and 6 to 12 ring carbons. Exemplary unsubstituted groups include phenyl, biphenyl and naphthyl. Exemplary substituents include one or more, preferably three or fewer, nitro groups, alkyl groups as described above, and/or one or more groups described above as alkyl substituents. Preferred aryl groups are unsubstituted aryl and hydroxyaryl.
The terms xe2x80x9cheterocycloxe2x80x9d or xe2x80x9cheterocyclicxe2x80x9d as used herein alone or as part of another group, denote optionally substituted fully saturated or unsaturated, aromatic or non-aromatic cyclic groups having at least one heteroatom in at least one ring, preferably monocyclic or bicyclic groups having 5 or 6 atoms in each ring. The heterocyclo group rmay, for example, have 1 or 2 oxygen atoms, 1 or 2 sulfur atomns, and/or 1 to 4 nitrogen atoms in the ring. Each heterocyclo group may be bonded through any carbon or heteroatom off the ring system. Preferred groups include those of the following formula, which may be bonded through any atom of the ring system: 
wherein r is 0 or 1 and T is xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94Nxe2x80x94R8 or xe2x80x94CHxe2x80x94R8 where R8 is hydrogen, alkyl, aryl or arylalkyl. Exemplary heterocyclo groups include the following: thienyl, furyl, pyrrolyl, pyridyl, imidazolyl, pyrrolidinyl, piperidinyl, azepinyl, indolyl, isoindolyl, quinolinyl, isoquinolinyl, benzothiazolyl, benzoxazolyl, benzimidazolyl, morpholinyl, piperazinyl, 4-alkylpiperazinyl, 4-alkylpiperidinyl, 3-alkpyrrolidinyl, oxazolyl, pyrazolyl, thiophenyl, pyridazinyl, thiazolyl, triazoyl, pyrimidinyl, 1,4-dioxanyl, benzoxadiazolyl, and benzofurazanyl. Exemplary substituents include one or more alkyl groups as described above and/or one or more groups described above as alkyl substituents.
The terms xe2x80x9chalogenxe2x80x9d or xe2x80x9chaloxe2x80x9d as used herein alone or as part of another group, denote chlorine, bromine, fluorine and iodine.
The term xe2x80x9cacylxe2x80x9d, as used herein alone or as part of another group, denotes the moiety formed by removal of the hydroxyl group from the group xe2x80x94COOH of an organic carboxylic acid. Exemplary groups include alkylcarbonyl, arylcarbonyl, or carbocyclo- or heterocyclocarbonyl. The term xe2x80x9cacyloxyxe2x80x9d, as used herein alone or as part of another group denotes an acyl group as described above bonded through an oxygen linkage (xe2x80x94Oxe2x80x94).
Peripherally-acting xcexa agonists can be prepared by the attachment of polar groups to non-peptide xcexa opioid receptor selective agonists, such as the arylacetamides. In designing the peripherally-acting ligands, the introduction of the polar groups may result in either retention or enhancement of antinociceptive potency and selectivity and also may increase the polarity of the ligand sufficient to reduce or eliminate CNS penetration across the blood-brain barrier (BBB). Thus, the identity and the positioning ofthe polar group(s) are important.
Using the prototypic arylacetamide, U50,488, as an example, the arylacetarnide pharmacophore can be divided into three regions: the aromatic region, the central region, and the amine region. All three regions represent potential positions for the attachment of polar groups. 
Compounds of formula (I) of the present invention are made as follows.
A series of novel compounds were made based on the class of arylacetarnides reported by Glaxo (J. Med. Chernm 1993, 36, 2075). Specifcally, compound 1 can be deprotected to yield intermediate 2, which can be derivatized by the attachment of a variety of polar groups (Scheme 1). 
The 3xe2x80x2-substituted series can be prepared via Scheme 2. The reduction of the Schiff base intermediate formed during the cyclization to 6 is expected to be stereoselective due to the directing effect of the neighboring hydroxymethyl group. Both intermediates 11 and 12 can be derivatized to confer peripheral selectivity.
The 5xe2x80x2-substituted series can be prepared via Schemes 3 and 4. Starting from Nt-Boc-O-MEM-D-serine, the 5xe2x80x2-(S) series can be prepared, and starting from from N-t-Boc-O-MEM-L-serine allows the preparation of the 5xe2x80x2-(R) series. 
wherein Ar, R1, R2, and n are defined in formula I. 
wherein Ar, R1, R2, and n are as defined in formula I. 
wherein Ar, R, R2, and n are as defined in formula I. 
wherein Ar, R1, R2, and n are as defined in formula I.
Using Schemes 1-4 the following exarnple compounds are rade.
Intermediate 3 can be treated with t-butyl bromoacetate and deprotected to produce {4-[1-(3,4-Dichlorophenyl)acetyl-2R-(1-pyrrolidinyl)-methyl]piperazinyl}acetic acid (26).
Intermediate 3 can be reacted with methane sulfonyl chloride to produce [1-(3,4-Dichlorophenyl)acetyl-4-methanesulfonyl-2R-(1-pyrrolidinyl)methyl]piperazine (27).
Intermediate 3can be coupled to N-t-Boc-L-aspartic acid-b-benzyl ester and deprotected to produce [4-S-Aspartic acid-a-amido-1-(3,4-dichlorophenyl)acetyl-2R-(1-pyrrolidinyl)methy]piperazine (28).
Intermediate 11 can be treated with t-butyl bromoacetate and deprotected to produce Methyl-[2Rxe2x80x94(O-2-acetic acid)hydroxymethyl-4-(3,4-dichlorophenyl)acetyl-3R-(1-pyrrolidinyl)methyl]-1-piperazinecarboxylate (29).
Intermediate 11 can be coupled to to N-t-Boc-L-aspartic acid-b-benzyl ester and deprotected to produce Methyl-[2Rxe2x80x94(Oxe2x80x94S-aspartic acid-a-acetyl)hydroxymethyl-4-(3,4-dichlorophenyl)acetyl-3R-(1-pyrrolidinyl)methyl]-1-piperazinecarboxylate (30).
Intermediate 12 can be treated with methanesulfonyl chloride to produce Methyl-[4-(3,4-dichlorophenyl)acetyl-2R(N-methanesulfonamido)amninomethyl-3R-(1-pyrrolidinyl)methyl]-1-piperazinecarboxylate (31).
Intermediate 12 can be coupled to 2Sxe2x80x94isothiocyanato-succinic acid-dibenzyl ester and deprotected to yield Methyl- {4-[3,4-dichlorophenyl]acetyl-3R-[1 -pyrrolidinyl]methyl-2R-[N-(succinic acid-2S-thioureido)]aminomethyl}-1-piperaainecarboxylate (32).
Intermediate 21 can be treated with t-butyl bromoacetate and deprotected to produce Methyl-[2Sxe2x80x94(Oxe2x80x942-acetic acid)hydroxymethyl-4-(3,4-dichlorophenyl)acetyl-5R-(1-pyrrolidinyl)methyl]-1-piperazinecarboxylate (33).
Intermediate 21 can be coupled to to N-t-Boc-L-aspartic acidxe2x80x94Sbenzyl ester and deprotec ted to produce Methyl-[2Sxe2x80x94(Oxe2x80x94Sxe2x80x94aspartic acid-a-acetyl)hydroxymethyl-4-(3,4-dichlorophenyl)acetyl-5R-(1-pyrrolidinyl)methyl]-1-piperazinecarboxylate (34).
Intermediate 22 can be treated with methanesulfonyl chloride to produce Methyl-[4-(3,4-dichlorophenyl)acetyl-2Sxe2x80x94(Nxe2x80x94methanesulfonamido)aminomethyl-5R-(1-pyrrolidinyl)methyl]-1-piperazinecarboxylate (35).
Intermediate 22 can be coupled to 2S-isothiocyanato-succinic acid-dibenzyl ester and deprotected to yield Methyl-{4-[3,4-dichlorophenyl]acetyl-5R-[1-pyrrolidinyl]methyl-2Sxe2x80x94[N-(succinic acid-2S-thioureido)]aminomethyl}-1-piperazinecarboxylate (36).
The 2R isomers of 33-34 and 35-36 can be prepared from intermediates 24 and 25, respectively to produce
Methyl-[2R-(0-2-acetic acid)hydroxymethyl-4-(3,4-dichlorophenyl)acetyl-5R-(1-pyrrolidinyl)methyl]-1-piperazinecarboxylate (37).
Methyl-[2Rxe2x80x94(Oxe2x80x94Sxe2x80x94aspartic acid-a-acetyl)hydroxymethyl-4-(3,4-dichlorophenyl)acetyl-5R-(1-pyrrolidinyl)methyl]-1-piperazinecarboxylate (38).
Methyl-[4-(3,4-dichlorophenyl)acetyl-2R-(Nxe2x80x94methanesulfonamido)aminomethyl-5R-(1-pyrrolidinyl)methyl]-1-piperazinecarboxylate (39).
Methyl-{4-[3,4-dichlorophenyl]acetyl-5R-[1-pyrrolidinyl]methyl-2R-[N-(succinic acid-2S-thioureido)]aminomethyl}-1-piperazinecarboxylate (40).
The corresponding structural formulas are shown hereunder. 
Compounds of formula II of the present invention are made by peripheralization by substitutions of the benzo portion of the tetrahydronaphthyl ring of DuPont series of compounds with polar groups. 
Starting material or precursors of the starting material are commercially available and thus allows regiospecific substitutions of the tetrahydronaphthyl ring (Scheme 5). While 5-hydroxytetralone, 6-hydroxytetralone, 7-hydroxytetralone, and 7-aminotetralone derivatives are readily available, 5-aminotetralone could be prepared from 5-hydroxytetralone (J. Org. Chem 1972, 37, 3570).
The tetralone derivatives can be converted to dihydronaphthyl derivatives and subjected to chemistry similar to that employed in the preparation of U50,488 derivatives. The resulting compounds are racemic mixtures that can be derivatized to confer peripheral selectivity. If necessary, the final compounds or one of the intermediates can be resolved to test both enantiomers. 
wherein R1, R2, and n are as defined in formula I.
Following the procedure shown in Schemes 5-7, the following example compounds are prepared.
Intermediate (xc2x1)-64 can be treated with t-butyl bromoacetate and deprotected to produce (xc2x1)-2-(3,4-dichlorophenyl)-N-methyl-N-1-[1,2,3,4-tetrahydro-5-(O-2-acetic acid)-hydroxy-2-(1-pyrrolidinyl)naphthyl]acetamide (72).
Intermediate (xc2x1)-65 can be treated with t-butyl bromoacetate and deprotected to produce (xc2x1)-2-(3,4-dichl6rophenyl)-N-methyl-N-1-[1,2,3,4-tetrahydro-7-(O-2-acetic acid)-hydroxy-2-(1-pyrrolidinyl)naphthyl]acetamide (73).
Intermediate (xc2x1)-66 can be treated with methanesulfonyl chloride to produce (xc2x1)-2-(3,4-dichlorophenyl)-N-methyl-N-1-[1,2,3,4-tetrahydro-7-(N-methanesulfonamido)-amino-2-(1-pyrrolidinyl)naphthyl]acetamide (74).
Intermediate (xc2x1)-67 can be treated with methanesulfonyl chloride to produce (xc2x1)-2-(3,4-dichlorophenyl)-N-methyl-N-1-[1,2,3,4-tetrahydro-5-(N-methanesulfonamido)-amino-2-(1-pyrrolidinyl)naphthyl]acetamide (75).
Intermediate (xc2x1)-68 can be treated with glycine benzyl ester and deprotected to produce (xc2x1)-2-(3,4-dichlorophenyl)-N-methyl-N-1-[1,2,3,4-tetrahydro-Sxe2x80x94(N-2-acetic acid)-carboxarnido-2-(1-pyrrolidinyl)naphthyl]acetarride (76).
Intermediate (xc2x1)-69 can be treated with glycine benzyl ester and deprotected to produce (xc2x1)-2-(3,4-dichlorophenyl)-N-methyl-N-1-[1,2,3,4-tetaahydro-5-(N-2-acetic acid)-sulfonamido-2-(1-pyrrolidinyl)naphthyl]acetamide (77).
Intermediate (xc2x1)-70 can be treated with glycine benzyl ester and deprotected to produce (xc2x1)-2-(3,4-dichlorophenyt)xe2x80x94N-methyl-N-1-[1,2,3,4-tetrahydro-7-(N-2-acetic acid)-carboxamido-2-(1-pyrrolidinyl)naphthyl]acetamide (78).
Intermediate (xc2x1)-71 can be treated with glycine benzyl ester and deprotected to produce (xc2x1)-2-(3,4-dichlorophenyl)-N-methyl-N-1-[1,2,3,4-tetrahydro-7-(N-2-acetic acid)-sulfonamido-2-(1-pyrrolidinyl)naphthyl]acetamide (79). 
The compounds of formula III of the present invention are prepared by substituting the central phenyl ring with polar groups. 
Compound 80 and analogues undergo a variety of diazonium-involving reactions for the attachment of polar groups (Scheme 7). 
Using the procedure shown in Scheme 7, the following compounds are made.
Interrnediate 81 can be treated with dibenzyl phosphoryl chloride followed by deprotection to produce 2-(3,4-dichlorophenyl)-N-methyl-N-{1-3-(O-phosphoryl)hydroxyphenyl-2-(1-pyrrolidinyl)ethyl}acetanmide (87).
Intermediate 85 can be coupled to methanesulfonyl chloride to produce 2-(3,4-dichlorophenyl)-N-methyl-N-{1-[3-(N-methanesulfonamido)aminomethyl]phenyl-2-(1-pyrrolidinyl)ethyl}acetamide (88).
Intermediate 85 can be coupled to 2S-isothiocyanato succinic acid and deprotected to produce 2-(3,4-dichlorophenyl)-N-methyl-N-{1-[3-(N-succinic acid-2S-thioureido)arninomethyl]phenyl-2-(1-pyrrolidinyl)ethyl}acetamide (89).
Intermediate 80 can be treated with dibenzyl phosphoryl chloride followed by deprotection to produce 2-(3,4-dichlorophenyl)-N-methyl-N-{1-3-(N-phosphoramido)aminophenyl-2-(1-pyrrolidinyl)ethyl}acetamide (90). 
87, R=xe2x80x94OPO3H2 
88, R=xe2x80x94CH2NHSO2Me
89, R=(S)xe2x80x94CH2NHC(S)NHCH(CO2H)CH2CO2H
90, R=xe2x80x94NHPO3H2 
The compounds of formula IV may be prepared by Scheme 8. 
wherein R1, R2, R3, and R4 are defined in formulas III and IV.
The diamino intermediate 91 (J. Med. Chem. 1990, 33, 286) can be coupled to different regioisomers of nitrophenylacetic acid, which are all commercially available. Reduction of the nitro group provides an amino group for the attachmnent of polar groups. Alternatively, the amino intermediates 95-97 readily undergo diazonium chemistry that converts the amino groups to carboxyl and sulfonyl chloride groups. This allows the polar groups to be attached via different linkers.
Following the procedure in Scheme 8, the following compounds are made.
Intermediate 96 can be treated with methanesulfonyl chloride to produce (xe2x88x92)-(5a,7a,8xcex2)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro-[4,5]dec-8-yl]-3-(N-methanesulfonamido)aminophenylacetaniide (104).
Intermediate 98 can be coupled to glycine benzyl ester and deprotected to yield (xe2x88x92)-(5a,7a,8xcex2)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro-[4,5]dec-8-yl]-3-(N-2-acid)sulfonamidophenylacetamide (105).
Intermediate 99 can be coupled to glycine benzyl ester and deprotected to yield (xe2x88x92)-(5a,7a,8xcex2)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro-[4,5]dec-8-yl]-3-(N-2-acid)carboxarnidophenylacetamide (106). 
Compounds of the above formulas may have one or more asymmetric carbon atoms. Pure sterochemically isomeric forms of the above compounds may be obtained, and diastereoisomers isolated by physical separation methods, including, but not limited to crystallization and chromatographic methods. Cis and trans diasteriomeric racemnates may be further resolved into their isomers. If separated, active isomers may be identified by their activity. Such purification is not, however, necessary for preparation of the compositions or practice of the methods herein.
As used herein, the compounds provided herein also include pharmaceutically acceptable salts, acids and esters thereof, stereoisomers, and also metabolites or prodrugs thereof that possess activity as analgesics but do not cause substantial CNS effects when administered or applied. Metabolites include any compound that is produced upon administration of the compound and metabolism thereof.
More detailed preparations of the compounds of the present invention follow. 
N-Benzyl-D-serine(1)1: To a mixture of D-serine (25.0 g, 0.237 mol) and 200 mL anhydrous methanol was added sodium cyanoborohydride (11.95 g, 0.190 mol), while maintaining the temperature at 0xc2x0 C. with an ice bath. Then, benzaldehyde (26.5 mL, 0.261 mol) was added to the reaction flask, dropwise, at 30xc2x0 C. The mixture was stirred for 60 Hr. at room temperature. Then, the mixture was filtered and rinsed with methanol (50 mL). The white solid was dried in a vacuum oven at 40xc2x0 C. and 10 minhg over 2 nights: 24.5 g. The filtrate was retained and the solvent was evaporated. This oil was passed through a silica gel column (10% MeOH/CH2Cl2) and 3.4 g of the desired compound was isolated. The total amount of the product was 27.9 g (60.0% yield). 1H NMR (DMSO-d6) xcex4 3.25 (m, 1H, CH), 3.85 (m, 2H, CH2), 4.11 (d, 2H, benzylic CH2), 7.45-7.53 (m, 5H, ArH).
Ref. (1) Ohfine, Y.; Kurokawa, N.; Higuichi, N.; Saito, M.; Hashimoto, M.; Tanaka, T. An efficient one-step reductive N-monoalkyation of xcex1-amino acids. Chemistry Letters. 1984, 441-444.
N-Benzyl-D-serine methyl ester(2): Hydrogen chloride (gas) was bubbled into anhydrous methanol for 10 minutes. Then, the solution was allowed to cool to room temperature. Then, N-benzyl-D-serine (24.6 gm, 0.126 mol) was added to the reaction flask and refluxed over night under dry nitrogen. Then, the solvent was evaporated and dissolved in dichloromethane (200 mL), and washed with a saturated solution of sodium bicarbonate. The dichloromethane layer was dried with magnesium sulfate and the solvent was evaporated. (23 gm, 87.2% yield). 1H NMR (CDCl3) xcex4 3.41 (d, 1H, CH), 3.52-3.80 (dd, 2H, benzylic), 3.69 (s, 3H, OMe), 7.27 (s, 5H, ArH).
N-[(1.1-Dimethylethoxy)carbonyl-D-Ser-(O-Bzl)-N-benzyl-D-Ser-OMe(3): To a solution of N-boc-D-serine-(O-bzl)OH (15 g, 50.76 mmol) in anhydryous dichloromethane (200 mL) was added HOBt (7.54 g, 55.8 mmol) at 0xc2x0 C. under dry nitrogen. Then, DCC (11.5 g, 55.7 mmol) in dichioromethane (100 mL) was added dropwise to the reaction flask. Then, this mixture was stirred for 1 Hr. Then, N-benzyl-D-serine-OMe (10 g, 47.8 mmol) in dichloromethane (100 mL) was added dropwise to the reaction flask. Then, stirred for 4 days. Then, filtered and rinsed with dichloromethane (100 ml). The white precipitate was DCU and HOBt. The filtrate was evaporated and re-dissolved in ethyl acetate (100 mL). Then, this was allowed to precipitate, overnightxe2x80x94more DCU. This was filtered and rinsed with ethyl acetate. Then, this was isolated on a silica gel colurnn (20% ethyl acetate/hexanes): an oil-17.3 g, 74.3% yield. 1H NMR (CDCl3) xcex4 1.43 (s, 9H, t-Bu), 3.54 (t, 1H, OH), 3.72 (s, 3H, OMe), 3.75 (dd, 2H, CH2) 3.79 (dd, 2H, CH2), 4.41 (d, 2H, CH2 benzylic), 4.43 (d, 2H, CH2 benzylic), 7.27-7.30(m, 10H, ArH).
(2R,R)-2-((Benzloxy methy)-5-(Hydroxymethyl)-4-(phenylmethyl)-3,6-piperazine dione(4)2: Into anhydrous chloroform (300 mL) was bubbled hydrogen chloride (gas). Then, the dipeptide (3) (13.5 g, 27.7 mmol) in chloroform (100 ml) was added to the reaction flask. The flask was stoppered and stirred for 64 Hr. Then, a saturated solution (100 ml) of sodium bicarbonate was added and stirred vigorously for 48 Hr. The cyclization was completed at this point. The organic layer was separated from the aqueous layer in a 1L separatory fimnel. The product was isolated from a silica gel column, eluting with dichloromethane-methanol-0.88 ammonia (96:2:2) to give (4) as an amorphous solid (6.0 g, 61.1% yield). 1H NMR (CDCl3) xcex4 3.72-3.96 (m, 7H), 3.97-5.24 (dd, 2H, CH2 benzylic), 4.45 (dd, 2H, CH2 benzylic), 7.15-7.30 (m, 10H, ArH); MS (FAB) m/e 355 (MH+).
Ref. (2) Williams, T. M; Ciccarone, T. Ma; MacTough, S. C. and et al. 2-Substituted pipeazincs as constrained amino acids. J. Med Chem. 1996, 39, 1345-1348. 
(2S,5S)-2-((Benzyloxy)methyl)-4-(phenylmethyl)-5-Diperazinemethanol(5): A suspension of lithium aluminum hydride (0.9 g, 23.7 mmol) in anhydrous tetrahydrofuran (40 mL) was treated with a solution of piperazinedione 4 (2.1 g, 5.92 mmol) in anhydrous tetrahydrofuran (200 mL). The reaction mixture was heated at reflux for 24 Hr and then, stirred at room temperature for 2 Hr. Water (10 ml) was added followed by aqueous sodium hydroxide (1N, 10 mL) and water (10 mL). The mixture was filtered, and the filtrate was evaporated to give 5 (1.67 g, 86.4% yield) as a viscous oil. 1H NMR (CDCl3)xcex42.58 (dd, 2H, CH2), 2.61 (t, 1H, OH), 3.10 (dd, 2H, CH2), 3.25 (dd, 2H, CH2), 3.50 (dd, 2H, CH2), 3.74 (s, 2H, CH2), 4.41 (dd, 2H, CH2 benzylic), 7.20-7.30 (m, 10H, ArH).
(2S,5S)-Methyl 2-[(Benzyloxy)methyl]-5-(hydroxymethyl)-4-(phenylmethyl-1-piperazine carboxclate (6)3: A solution of 5 (1.67 g, 5.11 mmol.) in acetonitrile (20 mL) was treated with a solution of methyl chloroformate (0.532 g, 5.63 mmol) in acetonitrile (10 mL) at 0xc2x0 C. The mixture was stirred at ambient temperature for 30 min., and then aqueous sodium carbonate solution (15 mL) was added. The organic solvent was removed, and the aqueous residue was extracted with chloroform (3xc3x9710 mL). The combined organic extracts were washed with aqueous sodium carbonate solution (10 mL), dried, and evaporated to give 6 (1.52 g, 77.3% yield) as an oil. 1H NMR (CDCl3) xcex4 2.54 (dd, 2H, CH2), 2.45 (t, 1H, OH), 2.72 (dd, 2H, CH2), 3.51 (dd, 2H, CH2), 3.67 (dd, 2H, CH2), 3.69 (s, 3H, OMe), 3.81 (dd, 2H, CH2), 4.44 (dd, 2H, CH2 benzylic), 7.17-7.31 (10H, ArH).
(3) Naylor, A.; Judd, D. B.; Lloyd, J. E.; Scopes, D. L. C.; Hayes, A. G.; Birch, P. J. A potent new class of k-Receptor agonist: 4-subtituted 1-(arylacetyl)-2-[(dialkylamino)methyl]piperazines. J. Med Chem. 1993, 36, 2075-2083. 
(2S,5S)-Methyl 2-[(Benzyloxy)methyl]-5-[(1-pyrrolidinyl)methyl]-4-(phenylmethyl-1-piperazinecarboxylate(7)3: A solution of oxalyl chloride (0.545 mL, 6.24 mmol) in dichloromethane (10 mL) at xe2x88x9265xc2x0 C. was treated with a solution of dimethyl sulfoxide (1.14 mL, 16.0 mmol) in dichloromethane (5 ml) maintaining the reaction temperature below xe2x88x9265xc2x0 C. The mixture was stirred at xe2x88x9270xc2x0 C. for 10 min, and then a solution of the piperazinemethanol (6: 2 g, 5.19 mmol) in dichloromethane (20 mL) was added at such a rate that the reaction temperature was maintained below xe2x88x9265xc2x0 C. The reaction mixture was stirred at xe2x88x9265xc2x0 C. for 3 Hr, and a solution of N-methylmorpholine (1.42 mL, 12.91 mmol) in dichworomethane (5 mL) was added. The mixture was stirred at xe2x88x9220 xc2x0 C. for 45 min and then washed with ice-cold hydrochloric acid (0.01 N, 100 mL and 50 mL), dried, evaporated, and placed on a high vacuum pump overnight. The residue was dissolved in methanol (10 mL) and was added to a solution of pyrrolidine (0.91 mL, 10.94 mmol) in methanol (10 mL) at xe2x88x9210xc2x0 C., which had been adjusted to pH 6.0 by the addition of methanolic hydrogen chloride. Sodium cyanoborohydride (0.67 g, 10.66 mmol) and 4-xc3x85 molecular sieves (0.66 g) were added, and the mixture was stirred at ambient temperature for 18 Hr. The mixture was filtered, and the filtrate was evaporated to dryness. The residue was dissolved in aqueous sodium carbonate (1M, 25 mL) and extracted with dichloromethane (2xc3x9750 mL). The product was isolated from a silica gel column, eluting with dichloromethane-methanol (98:2) to give (7: 1.0 g, 23.0% yield). 1H NMR (CDCl3) xcex4 1.75 (m, 4H, CH2CH2), 2.46 (m, 3H), 2.48(m, 4H, CH2CH2), 2.55 (dd, 2H, CH2), 2.70-2.85 (m, 3H), 3.41 (dd, 2H, CH2), 3.69 (s, 3H, OMe), 4.10 (m, 1H), 4.20 (m, 1H), 4.41 (dd, 2H, CH2 benzylic), 7.10-7.31 (m, 10H, ArH); MS (FAB) m/e 438 (MH+).
(3) Naylor, A.; Judd, D. B.; Lloyd, J. E.; Scopes, D. L. C.; Hayes, A. G.; Birch, P. J. A potent new class of k-Receptor agonist: 4-subtituted 1-(arylacetyl)-2-[(dialkylamino)methyl]piperazines. J. Med Chem. 1993, 36, 2075-2083. 
(2S,5S)-Methyl 2-(Hydroxymethyl)-5-[(1-pyrrolidiny)methyl]-1-pipterazine carboxylate(8): A solution of 7 (0.25 g, 0.571 mmol) in ethanol (200 mL) was hydrogenated over 10% palladium on carbon (Degussa type E101 NE/W) at 50 psi for 7 days. Then, filtered through celite and filtrate was evaporated. (0.13 g, 0.5 mmol: 87% yield).
(2S,5S)-Methyl 4-[(3,4-Dichloropheny)acetyl]-2-(hydroxy)methyl-5-[(1-pyrrolidinyl)methyl]-1-piperazinecarboxylate(9): To a solution of 1,1xe2x80x2-carbonyldiimiazole (0.20 g, 1.26 mmol) in dichloromethane (10 mL) was added portionwise 3,4-dichlorophenylacetic acid (0.25 g, 1.26 mmol) and the resulting solution stirred under nitrogen for 1 Hr, at room temperature. A solution of 8 (0.13 g, 0.5 mmol) in dichloromethane (10 mL) was added and the mixture at room temperature for 18 Hr. The reaction mixture was washed with sodium carbonate solution (2 N, 2xc3x9710 mL), dried, and evaporated to give a viscous oil. This material was dissolved in a mixture of tetrahydrofuran (5 mL) and water (5 mL) and treated with lithium hydroxide (42 mg, 1.0 mmol). The reaction mixture was removed, and the aqueous residue was extracted with dichloromethane (3xc3x9710 mL). The combined organic extracts were dried and evaporated to give a colorless gum which was purified by flash column chromatography on silica gel, eluting with ethyl acetate-methanol (40:1) to give 9 (155 mg, 70%) as a colorless foam.
Utilizing the above-denoted intermediates, the following compounds were prepared. 